The invention relates to a tunable high-frequency antenna which has, over its length dimension, a number of built-in switches by means of which antenna sections are defined and frequency matching takes place through antenna length tuning by disconnecting and connecting said antenna sections. Such an antenna is known from the specification DE-1949556.
The antenna specified in said specification is a so-called HELIX antenna in which sections of windings from the helical antenna radiator can be short-circuited by means of switches implemented as reed relays. The antennas usually operate in the UHF/VHF range in which the radiator is self-supporting. The monostable reed relays need a separate drive or feed line which has to be well screened from the antenna. For this purpose, they can be accommodated inside the tubular radiator of the HELIX antenna. The short-circuiting technique used in this case cannot be used for the much longer high-frequency wire antennas, all the more so because every switching component would require a feed line which will strongly couple to the high-frequency wire antenna. A further disadvantage is that a continuous current feed is required for every reed relay switched on.
Such a known antenna can also not be used for many applications, including military ones, for which only antennas composed of thin wires are suitable for reasons of visibility and weight. In the case of such an antenna, the antenna length also has to be matched to the frequency to obtain a good antenna efficiency since the bandwidth of such an antenna having a very large length/thickness ratio is very small with respect to the required frequency range.